Bed & Breakfast Rule Calculator
HMRC's 30-day bed and breakfast rule prevents investors from selling shares to crystallise a loss and immediately buying them back. If you sell shares and repurchase the same security within 30 calendar days, the disposal is matched against the repurchase — not your Section 104 pool. This often reduces or eliminates the tax loss you were trying to claim.
Use this free calculator to check if a specific sell-and-rebuy transaction triggers the B&B rule. Enter the details below to see your actual gain or loss based on the matched repurchase cost.
How to Interpret the Result
If the calculator shows “B&B Rule Triggered”, it means the disposal is matched against the repurchase under HMRC's 30-day rule. The allowable cost used to calculate your gain or loss is the cost of the repurchased shares — not the original cost from your Section 104 pool.
If the repurchase quantity is less than the sale quantity, only the repurchased quantity is B&B matched. The remainder of the disposal falls through to the Section 104 pool as normal.
Worked Example
You sell 200 shares of TSCO at £3.00 per share on 1 June (proceeds: £600). On 20 June (19 days later), you buy 200 shares at £2.80 per share (cost: £560). The B&B rule applies because the repurchase is within 30 days.
- Proceeds: 200 × £3.00 = £600
- Cost (B&B matched): 200 × £2.80 = £560
- Gain: £600 − £560 = £40
Without the B&B rule, the cost would have come from the Section 104 pool, which might have been significantly higher or lower.
For a deeper understanding of how this rule fits into the broader CGT framework, read our full guide on the 30-day bed and breakfast rule, including legitimate alternatives like bed-and-ISA and bed-and-spouse strategies.
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